Air valve pressure diaphragm carburetor

ABSTRACT

A carburetor having throttle and air intake valves and a booster venturi in both the primary and secondary air intake passages.

United States Patent Woods 1 Mar. 12, 1974 AIR VALVE PRESSURE DIAPHRAGM CARBURETOR [56] References Cited [76] Inventor: Stephen Woods, 311 Mason, UNITED STATES PATENTS Ann Arbor, Mich. 48103 2,136,959 11/1938 Winfield 261/36 A 2,454,974 11/1948 Mennesson 261/36 A [221 Med 1973 2,541,316 2 1951 Winkler 261/69 A 2 Appl No: 335 550 2,783,033 2/1957 Halik 261/36 A 3,322,408 5/1967 Stoltman. 261/50 A Related US. Application Data 3,232,587 2/1966 Nastas et a1. 261 /23 A {63] COnt-muatiomimpart of Sen NO 75539 Aug 7 3,272,482 9/1966 Carlson 261/50 A 97 abandoned which i a i i p f 3,279,767 10/1966 Stoltman 261/50 A Ser. NO. 846,563, July 31, 1969, Pat. NO. 3,618,904, 3,317,195 5/1967 Blckhaus A which is a Conlinumiomimpflrt of No 22 3,432,152 3/1969 Sweeney .1 261/39 B 3,575,388 4/1971 Scarr, Jr. 261 69 A April 9, 1969, Pat. No. 3,556,067, which is a continuation-impart of Ser. No. 629,488, April 10, 1967, abandoned,

US. Cl 261/23 A, 261/23 A, 261/36 A, 261/39 A, 261/39 B, 261/39 C, 261/50 A, 261/67, 26'1/51, 261/52, 261/78 R, 261/69 A, 26l/D1G.50, 261/DIG. 39

Int. Cl. F02m 7/16 Field of Search... 261/23 A, 36 A, 39 A, 39 B, 261/39 C, 50 A, 67, 52, 51, 69 A, DIG. 50

Primary Examiner-Tim R. Miles Attorney, Agent, or Firm-William H. Griffith ABSTRACT 17 Claims, 7 Drawing Figures PAIENIEIJIIAII I 2 B74 SHEET 2 [1F 3 AIR VALVE PRESSURE DIAPHRAGM CARBURETOR REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of my copending application, Ser. No. 175,539, filed Aug. 27, 1971, now abandoned, which application, Ser. No. 175,539 is a continuation-in-part of my application, Ser. No. 846,563 filed July 31, 1969 and now U.S. Pat. No. 3,618,904, which application, Ser. No. 846,563 was a continuation-in-part of my application, Ser. No. 822,828, filed Apr. 9, l969 and now US. Pat. No. 3,556,067, which application, Ser. No. 822,828 was a continuation-in-part of my application, Ser. No. 629,488 filed Apr. 10, 1967 and now abandoned.

SUMMARY OF THE INVENTION One object of this invention is to provide a carburetor designed to accurately control wide'open, partthrottle and idle fuel and air requirements.

Another object is to provide a carburetor designed to minimize hydrocarbon emission with substantially no loss in power or performance and with improved econ orny.

Another object is to provide a high dispersion booster venturi nozzle which is especially designed to vaporize or break up and disperse fuel entering the air intake passage.

Another object is to provide means for increasing the velocity of air in the air intake passage to achieve better fuel dispersion.

Another object is to provide means for controlling the admission of fuel to the secondary air intake passage designed to prevent premature fuel dumping when the throttle is opened suddenly.

Another object is to provide means for balancing the pressures in the primary and secondary fuel chambers to reduce fuel surges in the secondary fuel supply system particularly when the secondary fuel inlet valve opens and closes.

Other objects and features of the invention will become apparent as the following description proceeds, especially when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a top plan view of a carburetor constructed in accordance with my invention but with the primary and secondary air valves omitted so as to expose the venturi boosters in the primary and secondary air intake passages.

FIG. 2 is a front view of the carburetor with parts shown in section and parts in elevation.

FIG. 3 is an enlarged fragmentary top plan view showing a venturi booster.

FIG. 4 is a sectional view taken on the line 4-4 in FIG. 3.

FIG. 5 is an enlargement of a portion of FIG. 1'.

FIG. 6 illustrates a modification.

FIG. 7 illustrates a further modification.

' or pin 22 upstream of the throttle plate 19 and booster Referring now more particularly to the drawings, the

' it will be understood that the invention is also applicable to one and two-barrel carburetors.

The carburetor has two primary air intake passages 13P and two secondary air intake passages 13S. Only one of the primary intake passages and one of the secondary air intake passages and their associated parts will be described in detail, although it should be understood that the other primary and secondary air intake passages and their associated parts may be the same as those described.

The primary and secondary air intake passages 13? and are formed by adjacent vertical bores in the housing 1. The passages 13F and 135 are separated by the housing wall 15. The air intake passage 13F is controlled by a suitably actuated throttle valve' plate 19 therein secured to a pivotal shaft or pin 19. The primary throttle plate 19 is shown at off-idle and may move from off-idle through part throttle to wide open position in which it is disposed substantially vertically in the passage.

The wall of primary air intake: passage 13? is provided intermediate its ends with an annular restriction forming a main venturi 20P for the air flow. A booster venturi 21F, more fully described hereinafter, of greater restriction than the main venturi 20F is disposed in the throat of the main venturi.

A primary air valve 22P is secured to a pivotal shaft venturi 21P adjacent the top of the primary air intake passage 13P. The air valve 22? may move from the closed position illustrated to a fully open substantially vertical position.

The air valve 22F is subject to the depression '(vacuum) in the air intake passage and also to the position of the throttle valve 19. A lever 23 is secured to the shaft 19' of the throttle valve 19 and a lever 24 is secured to the shaft 22 of the air valve 22P. A rod 25 is pivoted to lever 23 and has a spring-biased lost motion connection with the lever 24. This lost motion isprovided by a pin 26 movable in an arcuate slot 27 in lever 24 which is centered on the axis of pin 22'. The pin has an abutment 28 which is slidabl-e on rod 25. A coil spring 29 on rod 25 is compressed between a fixed abutment 30 on the rod and the sliding abutment 28 to impose a yielding bias tending to close the air valve. Nut 31 threaded on the end of rod 25 is to retain abutment 28 and may be threaded either way to change the compression on spring 29. Obviously this yielding bias is reduced or partially relieved by the counterclockwise opening movement of the throttle valve. The yielding bias permits the air valve to move in opening and closing directions in response to changes in the depression (vacuum) in the air intake passage; The slot 27 allows the air valve 22P to move in a closing direction by diffuel inlet 6? past a fuel control valve 7P. The fuel control valve 7P includes a cylinder 7a having an elongated, axially movable needle valve 712 therein projecting through an orifice 7c. The needle valve 7b has a head 7d adapted to close the orifice and is normally urged to closed position by a calibrated spring AP bearing at one end against the head 7d and at the other end against the wall of the cylinder 7a. The needle valve 7b also has a stem 7e projecting from the head 7d and engageable with the diaphragm SF. The inlet 6P opens into the interior of the cylinder 7a but fuel from the inlet enters the chamber 2P only when the needle valve 7b is opened by the movement of the diaphragm P to the left in FIG. 2.

The primary system 3 has a main jet 23? leading to the fuel passages 24F and 25F. The passage 25F leads to the booster venturi 21F and the passage 24? leads to the idle ports 27 and 28. Idle ports 27 and 28' are open to manifold vacuum in the curb-idle position of the throttle plate 19 to provide a proper fuel mixture. The size of the idle port 28 is controlled by an idle adjustment screw 29P.

The diaphragm SP is exposed to the pressure Within the fuel chamber 2P on one side and to atmospheric pressure on the other side, and is movable in response to differential pressure. Movement of the diaphragm 5? to the left in FIG. 2 will move the needle valve 7? to the left and open orifice 70 so that fuel can flow into chamber 2P.

A mechanical linkage is provided to control the needle valve 7b in response to movement of the throttle valve 19. This linkage is indicated at 46? and includes a lever 47P pivoted at its upper end at 60F to the cover plate 9P. Intermediate its ends, the lever has an abutment 61P engageable with, but not secured to, a member 62P on the outer side of the diaphragm 5P. At its lower end, the lever 47P is pivoted to the outer end of a push rod 48P which extends and slides through an opening in a housing plate lb. The inner end of push rod 48? engages a cam 50P secured to and rotatable with throttle plate shaft 19 so that the cam turns with the throttle plate. A coil spring 64P compressed between the housing plate lb and a flange 63? on push rod 48P holds the inner end of the push rod in contact with-the cam 5UP. Rotation of the throttle plate 19 will rotate the cam SOP and since the inner end of the rod 481 is in contact with the cam profile, the position of the throttle plate 19 will determine the angular position of the lever 47P.

Referring to the secondary system 4, a secondary throttle plate 368 is secured to a pivotal shaft or pin 36 in the secondary air intake passage 13S adjacent the lower end thereof. Throttle plate 368 is movable from the closed position shown in solid lines to an open substantially vertical position. The primary throttle plate shaft 19' has a lever 33F connected to it, and a lever 358 is connected to the secondary throttle plate 365.

One end of a rod 345 is pivoted to the lever 33! and the other end has a slidable pivotal connection in slot 395 in the lever 358 to provide a lost motion connection between the primary and secondary throttle plates.

An air valve 375 secured to pivotal shaft or pin 37 is disposed adjacent the top of the secondary air intake passage 13$ for movement from the closed position shown to an open substantially vertical position. The secondary air valve 375 is normally closed but opens in response to increasing depression (vacuum) in the air intake passage 138. Engine manifold vacuum is applied to the air intake passage 138 when the secondary air valve 365 opens. Depending upon the particular engine requirements, the responsiveness of air valve 375 to differential air pressure, and thus its opening rate can be controlled. It is preferable to avoid sudden snap-like opening of the secondary air valve 375. For this purpose control means are provided to govern or dampen the opening rate of the air valve 375, such control means in this instance being shown as a plurality of pressure relief openings 408 in the air valve which allow air to pass through at a predetermined calibrated rate. This reduces the initial force exerted on air valve 378 when secondary throttle plate 365 is opened, and also provides a controlled initial rate of opening.

There is an annular restriction forming a venturi 205 in passage 13S and a booster venturi 218 in the throat of the venturi 205.

Fuel is supplied to the secondary system from a fuel receiving portion which is substantially the same as the fuel receiving portion previously described and accordingly the same reference numerals with the suffix S instead ofP are employed. Thus the fuel chamber 28 is defined in part by a cavity in the housing and in part by the flexible diaphragm 58 which is clamped over an opening in the cavity by the cover plate 98. The fuel chamber 28 is a completely closed reservoir unvented to the atmosphere.

The fuel control valve 78 controls the admission of fuel to the chamber 25 from the fuel inlet 65. The parts of this fuel valve 78, namely the portions 7a-7e are the same as those previously described in connection with the fuel valve 7P and function in the same manner, and the needle valve 7b is acted upon by a similar calibrated spring AS.

The secondary system 4 has a main jet 235 leading to fuel passages 24S and 258. The passage 25S leads to the venturi booster 21S and the passage 24S leads to the secondary idle port 51.

The diaphragm SS is exposed to the pressure within the fuel chamber 28 on one side and to atmospheric pressure on the other side, and is movable in response to differential pressure. Movement of the diaphragm 55 to the right in FIG. 2 will move the needle valve 7b of fuel valve 75 to the right and open orifice so that fuel can flow into chamber 25.

The mechanical linkage 46$ for controlling the opening of the needle valve of fuel valve includes the lever 47S pivoted at its upper end at 605 to the cover plate 98, which lever has an abutment 61S spaced from the pivot and engageable with but not connected to the member 625 on the outer side of the diaphragm 55.

The lever 478 has a lost motion connection with the secondary air valve 375. A link 408 is secured to shaft 37 so as to turn with the air valve 375. A rod 415 is pivoted to the link 40S and slides through a sleeve 428 in the lever 478. A compression coil spring 435 encircles the rod between an abutment 448 on the end of the rod and the sleeve 428 on the lever. In the closed position of the air valve 378 shown in FIG. 2, the lost motion connection will hold the lever 478 in substantially the position shown. It will be apparent that counterclockwise opening movement of the air valve will, through the resilient lost motion connection, impose a yielding force on the lever 47S tending to move it counterclockwise and move diaphragm 58 to the right thereby opening the needle valve 7b.

The venturi booster 21? is shown in FIGS. 3 and 4. The venturi booster 218 is of the same construction.

The booster venturi 21F is in the form of a tubular or ring-shaped body having a central through passage 199 aligned with the air intake passage 131. This passage has a restriction at the upper end providing a venturi 203. A circular channel 200 in the venturi booster encircles the passage 199 at or slightly below the venturi 203 and receives fuel from passage P. Small axially extending venturi openings 201 extend into the channel 200, and axially extending slightly flaring openings 202, aligned with openings 201, extend downward from the channel 200 into the enlarged exit portion 198 of the passage 199. Fuel moving around the channel 200 is broken up and dispersed by the fast moving air in openings 201 ,and 202 carried into the exit portion 198 of passage 199.

Horizontal holes 204 provide communication between the channel 200 and the passage 199 adjacent the restriction or venturi 203. The restriction terminates in an annular'depending lip 205 which partially overlaps the openings 204 to increase the venturi effect and draw fuel from the channel 200 into the air passage 199 by the depression (vacuum) at this point in the air passage.

It will thus be seen that a high degree of atomization or breakup and dispersion of fuel in the circular channel 200 is achieved. The air moving through the axial openings 201 and 202 carries the dispersed fuel with it into the air intake passage 13?. Simultaneously, air passing the venturi 203, which is the throat of a pezometer ring, also draws fuel by way of the cross-holes 204 into the passage 199. Accordingly, fuel is dispersed by both the vertical passages 201 and horizontal passages 204 to .atomize the liquid fuel into a homogeneous airfuel mixture.

A fuel line 98 is shown in FIG. 1 having one end 99 adapted to receive fuel from the tank by a fuel pump. The other end' of the line which is a return line to the fuel tank has a restriction 100. The fuel inlets 6? and 65 to the fuel chambers communicate in sequence with the fuel line 99. This arrangement, including the restriction, reduces the amount of fuel surging in the fuel supply system when the secondary needle valve 712 opens and closes. Also, this arrangement reduces surging on sudden heavy demand when otherwise the secondary system might lag and substantially all of the fuel initially be supplied to the primary system.

A balance tube or passage 101 having a restriction 102 connects the fuel chambers 2P and 23. This arrangement serves to balance pressures in the two chambers and also assists in reducing surges in the fuel supply system when the secondary needle. valve 7b opens and closes. It also assists in eliminating a tendency for the secondary system to lag on sudden heavy demand and all of the fuel initially to go to the primary system.

In operation, when the engine is turned over during starting, fuel under pressure from the fuel tank and line 98 enters the fuel inlet passages GP and 6S and fills the passages completely up to fuel valves 7? and 78. The excess fuel passes through restriction 100 and returns to the fuel tank. The primary air valve 22P is normally in a closed position when the engine is not operating and throttle plate 19 is in the curb-idle position. Cranking the engine induces a depression (vacuum) which is sensed at idle ports 27, 28 and 51, as well as at the primary venturi booster 21?. This depression (vacuum) is transmitted through the respective channels and passages 24P, 25F and 248 through the main jets 23F and 23S to the chambers 21' and 28. The depression (vacuum) in chambers 2? and 2S forces the diaphragms SP and 58 to move or flex inwardly pushing needle valves 7b inwardly against the tension of calibrated springs AP and AS, opening the orifices 7c and allowing fuel to flow from the inlets into chambers 2? and 25. The fuel in chambers 2? and 25 is then transmitted through the main jets 231 and 238 to the respective passages 24?, 245 and 25F. Thus fuel initially enters the air stream through idle ports 27', 28', 51 and booster venturi 21P. Fuel does not initially flow from booster venturi 215 because secondary throttle plate 368 and secondary air valve plate 378 are closed at this time.

As the engine idles the primary air valve plate 221 opens slightly, depending on the pre-load and tension of the calibrated primary air valve spring 29 'to allow air to enter. The degree of opening of primary air valve 22P is a function of the rate and tension of the spring 29 which is calibrated for specific air demands. The lighter the pre-loadand rate of spring 29, the greater the amount of airsupplied to the engine.

As primary throttle plate 19 opens wider, the primary airvalvecontrol rod 25 reduces the tension on spring 29 allowing the primary air valve 22F to open further, leaning out the air-fuel mixture and still maintaining high air velocities.

The provision of the primary air valve 22P maintains high air velocities in the primary system at curb-idle, off-idle and low part-throttle (30-40 miles per hour) engine operations so as to achieve a high degree of fuel vaporization and homogeneity of fuel-air mixtures and the entry of the fuel-air mixture into the cylinders of the engine at high air velocities. As a result, a lean homogeneous mixture is achieved reducing overall pollutant emissions. The primary air valve functions to provide these high air velocities until it reaches a substantially vertical position in the air intake passage, which is at a part-throttle position of the throttle plate 19 where secondary throttle plate 365 begins to open, and

is inoperative thereafter.

At the curb-idle position of throttle plate 19, the engine vacuum at idle ports 27, 28 and 51 is high. This high depression (vacuum) is transmitted by the passages 24P, 24S and 25P tothe diaphragms SP and 5S and produces a corresponding inward movement thereof. The amount which the diaphragms move at curb-idle is governed by engine depression only and is not controlled through the mechanical linkages 46F and 46S.

As the throttle plate 19 is opened wider from curbidle, the movement of air through the air passage 13P draws fuel from the booster venturi 21?. The depression (vacuum) in the fuel passages is further reduced and in turn the diaphragms SP and 55 move outward by differential pressure and the needle valves 7b begin to close. However, the mechanical linkage 46P prevents the diaphragm 5P from moving outward far enough to close the needle valve and maintains a constant linear relationship between the fuel requirements of the engine and the air flow through the carburetor at all positions of the throttle plate 19 other than curb-idle, namely, off-idle, part-throttle and wide-open throttle. For a given position of throttle plate 19 other than curb-idle, a minimum needle valve position of valve 7P is maintained mechanically by the action of the linkage 461. The amount of opening of the needle valve 7b of valve 7? is governed by the profile of cam SOP and the lever ratio of lever 47P.

The rate and amount of opening of the needle valve of valve 7P is transmitted mechanically from the outer or atmospheric side of the diaphragm P. This mechanical linkage provides the minimum fuel delivery necessary to operate the engine at the lowest permissible hy drocarbon levels. If the velocity of air passing the booster venturi 21F and the depression (vacuum) at idle ports 27 and 28 should increase to an amount greater than normally encountered at a specific throttle opening, the diaphragm SP is permitted to flex inwardly away from the lever 47? by differential pressure allowing a richer mixture in order to maintain a combustible fuel and air mixture to the engine maintaining a constant power output in relation to air consumption demand. However, the differential pressure acting on the diaphragm cannot lean out or reduce the fuel delivery below that which cam 50P is designed to deliver.

During initial opening of throttle plate 19, secondary throttle plate 365 remains closed due to the lost motion built into the linkage 33S-35S. At an intermediate position of the throttle plate 19F, called the pick-up point, the linkage causes secondary throttle plate 368 to begin to open. By varying the construction of the linkage, the rate of opening of plate 368 relative to plate 19 can be changed to provide different fuel-air mixtures atdifferent loads and engine speeds to suit performance requirements.

As secondary throttle plate 368 opens, secondary air valve 37S is subjected to increased downward air pressure tending to open it from its generally closed position. As this occurs, additional air flow is generated through secondary air passage 138. As before stated, control means are provided to govern or dampen the opening rate of the secondary air valve 37S, here shown as comprising the relief openings 405. This reduces the initial force on the secondary air valve 378 when the secondary throttle plate 368 is open and also provides a controlled initial rate of opening.

The opening of the secondary throttle plate 36S results in an increase in manifold depression (vacuum) transmitted through the secondary venturi booster 21S and passage 255 due to the closed position of the secondary air valve 378. This higher depression is transmitted through the main metering jet 238 to the secondary diaphragm 5S. The diaphragm 5S responding to this higher depression (vacuum) moves the secondary needle valve 7b inward to allow additional fuel to enter chamber 25 and then via the main jet 23S and the booster venturi 218 to enter the engine. When the depression (vacuum) below the secondary air valve 37S reaches a sufficient magnitude, the secondary air valve begins to open allowing additional air to enter the secondary air intake 135. The rate of opening of the secondary air valve 37S is a function of the rate and tension of the calibrated spring 43S which opposes such opening movement. The opening of the secondary air valve 378 in turn moves the lever 47S counterclockwise by a yielding pressure applied through spring 438. Such movement of the lever 47S shifts the diaphragm 5S further inwardly to cause needle valve 7b to allow greater amounts of fuel to enter the chamber 28 and ultimately to flow into the secondary air intake passage 215. As secondary air valve 378 continues to open in response to differential pressure, the lever 475 is turned further in a counterclockwise direction by the yielding force of spring 435 to allow even greater amounts of fuel to enter the secondary system.

FIG. 6 shows a modification incorporating a temperature compensation device. The pin 19' to which the throttle valve plate 19 is secured acts upon the lower end of the rod 25 through a cam 300 and spring strip in the form of a temperature sensitive bimetal strip 302. One end of the bimetal strip 302 is secured to the carburetor housing 1 by a fastener 304 and the other end of the bimetal strip is pivotally connected to the lower end of the rod 25 where indicated at 306. The cam 300 is secured to pin 19 beneath an intermediate portion of the bimetal strip to permit its end306 to descend when the pin 19' turns counterclockwise to open the throttle valve plate 19 thereby causing the rod 25 to descend and reduce the closing bias on the primary air valve 22P. Conversely, clockwise turning of pin 19 back to the illustrated position to close throttle valve plate 19 will raise the end 306 of bimetal strip 302 and also the rod 25, increasing the closing bias on the primary air valve 22F. A decrease in temperature tends to straighten the bimetal strip, having the effect of raising its end 306 attached to the rod 25, whereas an increase tends to warp it further than that illustrated to lower its end attached to the rod. Raising the end of rod 25 due to a temperature drop increases the tension in spring 29, whereas lowering rod 25 due to a temperature rise decreases the tension in spring 29. Thus the bias of the lost-motion connection is increased by a drop in temperature and is decreased by a rise in temperature.

FIG. 7 illustrates a modification of the FIG. 6 construction in which the temperature compensation device 311 is incorporated in the rod 25. In the FIG. 7 modification, the spring strip 302 (not shown) is not a bimetal member having temperature sensitive characteristics as in FIG. 6, but is merely an ordinary spring strip element which may be otherwise identical in appearance to the element shown in FIG. 6. The temperature compensation device 311 comprises a capsule including cylinder 310 having the upper end secured to the upper end portion 25A of the rod 25. The lower end portion 258 of the rod 25 is connected at the bottom to spring strip 302 as in FIG. 6, and extends upwardly through the bottom end wall of the cylinder and has a piston 312 on its upper end slidable within the cylinder. A body of thermally expansible material 316 is contained within the lower end portion of the cylinder beneath the piston. The bottom wall of the cylinder seals around rod portion 25B to prevent escape of the thermally expansible material 316. A coil spring 314 is compressed between the piston 312 and the upper end of the cylinder to hold the piston pressed against the body of thermally expansible material 316. An air vent 313 in the upper end of the cylinder prevents air from being trapped therein. The thermally expansible material 316 expands in response to an increase in temperature thereby decreasing the effective length of the rod 25 and correspondingly decreasing the tension in spring 29. Such material contracts in response to a decrease in temperature thereby increasing the effective length of rod 25 and correspondingly increasing the tension in spring 29. Thus the bias in the lost-motion connection is increased by a drop in temperature and is decreased by a rise in temperature.

I claim:

1. In a carburetor, an air intake passage, a throttle valve controlling said air intake passage, a fuel passage leading into said air intake passage, an air valve in said air intake passage upstream from said throttle valve, and yieldable means urging said air valve to closed position, said air valve being adapted to open against the action of said yieldable means in response to vacuum in said air intake passage, said yieldable means including a rod connected to said throttle valve, a pin having a lost-motion connection with said air valve, spring means between said rod and pin, and means for adjusting the tension of said spring means.

2. In a carburetor, primary and secondary systems respectively having primary and secondary air intake passages, throttle valve means controlling said primary and secondary air intake passages, primary and secondary closed fuel chambers, primary and secondary fuel passages respectively leading from said primary and secondary fuel chambers to said primary and secondary air intake passages, primary and secondary fuel inlet passages to said respective primary and secondary chambers, fuel valves controlling the flow of fuel respectively from said primary and secondary fuel inlet passages to said primary and secondary fuel chambers, a fuel line leading from a source of fuel under pressure and communicating with said fuel inlet passages in sequence and then leading back to the source and a restriction in the portion of saidfuel line leading back to the source.

3. In a carburetor, primary and secondary systems respectively having primary and secondary air intake passages, throttle valve means controlling said primary and secondary air intake passages, primary and secondary closed fuel chambers, primary and secondary fuel pas sages respectively leading from said primary and secondary fuel chambers to said primary and secondary air intake passages, primary and secondary fuel inlet passages to said respective primary and secondary chambers, fuel valves controlling the flow of fuel respectively from said primary and secondary fuel inlet passages to said primary and secondary fuel chambers, and pressure balance tube passage means connecting said primary and secondary chambers balancing pressures therein and placing the same in communication with one another.

4. The structure defined in claim 3, wherein said balance tube passage means has a restriction therein.

5. In a carburetor, an air intake passage, a throttle valve controlling said air intake passage, a fuel passage leading into said air intake passage, an air valve in said air intake passage upstream from said throttle valve, and yieldable means urging said air valve to closed position, said air valve being adapted to open against the action of said yieldable means in response to vacuum in said air intake passage, said yieldable means inc'luding a rod connected to said throttle valve, a pin having a lost-motion connection with said air valve, and spring means between said rod and pin.

6. In a carburetor, a primary air intake passage, a primary throttle valve controlling said air intake passage, a primary fuel passage leading into said air intake passage, a primary air valve in said air intake passage upstream from said throttle valve adapted to open in response to vacuum in said air intake passage, means providing a connection between said throttle valve and said air valve to open said air valve in response to open ing movement of said throttle valve, said connection means including spring means imposing a yielding clos 10 ing bias on said air valve with a force dependent upon the position of said throttle'valve.

7. The structure defined in claim 6, wherein said connection means includes a first member connected to one of said valves, a second member connected to the other of said valves, and spring means between said first and second members.

8. In a carburetor, a primary air intake passage, a primary throttle valve controlling said air intake passage, a primary fuel passage leading into said air intake passage, a primary air valve in said air intake passage upstream from said throttle valve adapted to open in response to vacuum in said air intake passage, means providing a connection between said throttle valve and said air valve to open said air valve in response to opening movement of said throttle valve, said connection means including spring means imposing a yielding closing bias on said air valve when said throttle valve is in curb-idle position, said air valve being substantially fully open when said throttle valve is at a part-throttle position.

9. The structure defined in claim 8, including a secondary air intake passage, a normally closed secondary throttle valve in said secondary air intake passage, a secondary air valve in said secondary air intake passage upstream from said secondary throttle valve adapted to open in response to vacuum in said secondary air intake passage, a secondary fuel passage leading to said secondary air intake passage between said secondary throttle valve and said secondary air valve, and a lostmotion connection between said primary throttle valve and said secondary throttle valve to open said secondary throttle valve in response to opening movement of said primary throttle valve past said part-throttle position in which said primary air valve is substantially fully open.

10. The structure defined in claim 9, including a secondary fuel valve controlling the flow of fuel to said secondary fuel passage, means subject to the vacuum in said secondary air intake passage for moving said fuel valve in an opening direction in response to an increase in vacuum and in a closing direction in response to a decrease in vacuum, and means for maintaining said secondary fuel valve open a predetermined minimum amount dependent upon the position of said secondary air valve regardless of the vacuum in said secondary intake passage.

1].. In a carburetor, a primary air intake passage, a primary throttle valve controlling said primary air intake passage, a fuel passage leading to said primary air intake passage, a secondary air intake passage, a normally closed secondary throttle valve in said secondary air intake passage, a secondary air valve in said secondary air intake passage upstream from said secondary throttle valve, a secondary fuel passage leading to said secondary air intake passage between said secondary throttle valve and said secondary air valve, a fuel valve controlling the flow of fuel to said secondary fuel passage, means subject to the vacuum in said secondary air intake passage for moving said fuel] valve in an opening direction in response to an increase in vacuum and in a closing direction in response to a decrease in vacuum, and means for maintaining said secondary fuel valve open at least a predetermined amount dependent upon the position of said secondary air valve regardless of and independently of the vacuum in said secondary air intake passage.

12. In a Carburetor, a primary air intake passage, a primary throttle valve controlling said primary air intake passage, a fuel passage leading to said primary air intake passage, a secondary air intake passage, a normally closed secondary throttle valve in said secondary air intake passage, a secondary air valve in said secondary airintake passage upstream from said secondary throttle valve, a secondary fuel passage leading to said secondary air intake passage between said secondary throttle valve and said secondary air valve, a fuel valve controlling the flow of fuel to said secondary fuel passage, means subject to the vacuum in said secondary air intake passage for moving said fuel valve in an opening direction in response to an increase in vacuum and in a closing direction in response to a decrease in vacuum, and means for maintaining said secondary fuel valve open a predetermined amount dependent upon the position of said secondary air valve regardless of the vacuum in said secondary air intake passage; said lastmentioned means including a member movable in one direction to open said fuel valve, and a yieldable connection between said secondary air valve and said member.

13. In a carburetor, a primary air intake passage, a throttle valve controlling said air intake passage, a fuel passage leading into said air intake passage, an air valve in said air intake passage upstream from said throttle valve adapted to open in response to vacuum in said air intake passage, yieldable means resisting opening movement of said air valve with a force dependent upon the position of said throttle valve, and means for increasing the force of said yieldable means in response to a decrease in temperature and for decreasing the force of said yieldable means in response to an increase in temperature.

14. In a carburetor, a primary air intake passage, a throttle valve controlling said air intake passage, a fuel passage leading into said air intake passage, an air valve in said air intake passage upstream from said throttle valve adapted to open in response to vacuum in said air intake passage, yieldable means resisting opening movement of said air valve with a force dependent upon the position of said throttle valve, said yieldable means including a rod, a pin having a lost-motion connection with said air valve, spring means between said rod and pin adapted to apply a closing bias on said air valve through said pin, a connection between said rod and throttle valve including a temperature sensitive element, said element upon a drop in temperature moving said rod to increase the tension of said spring means and hence the closing bias on said air valve and upon a rise in temperature moving said rod to decrease the tension of said spring means and hence the closing bias on said air valve.

15. The structure defined in claim 14, wherein said temperature sensitive element is a bimetal strip.

16. In a carburetor, a primary air intake passage, a throttle valve controlling said air intake passage, a fuel passage leading into said air intake passage, an air valve in said air intake passage upstream from said throttle valve adapted to open in response to vacuum in said air intake passage, yieldable means resisting opening movement of said air valve with a force dependent upon the position of said throttle valve, said yieldable means including a rod, a pin having a lost-motion connection with said air valve, spring means between said rod and pin adapted to apply a closing bias on said air valve through said pin, means providing a connection between said rod and throttle valve, and a temperature sensitive device incorporated in said rod operable to alter the effective length of said rod in response to temperature changes such that the tension of said spring means and hence the closing bias thereof is increased upon a drop in temperature and is decreased upon a rise in temperature.

17. The structure defined in claim 16, wherein said temperature sensitive device is a capsule containing a thermally expansible material. 

1. In a carburetor, an air intake passage, a throttle valve controlling said air intake passage, a fuel passage leading into said air intake passage, an air valve in said air intake passage upstream from said throttle valve, and yieldable means urging said air valve to closed position, said air valve being adapted to open against the action of said yieldable means in response to vacuum in said air intake passage, said yieldable means including a rod connected to said throttle valve, a pin having a lostmotion connection with said air valve, spring means between said rod and pin, and means for adjusting the tension of said spring means.
 2. In a carburetor, primary and secondary systems respectively having primary and secondary air intake passages, throttle valve means controlling said primary and secondary air intake passages, primary and secondary closed fuel chambers, primary and secondary fuel passages respectively leading from said primary and secondary fuel chambers to said primary and secondary air intake passages, primary and secondary fuel inlet passages to said respective primary and secondary chambers, fuel valves controlling the flow of fuel respectively from said primary and secondary fuel inlet passages to said primary and secondary fuel chambers, a fuel line leading from a source of fuel under pressure and communicating with said fuel inlet passages in sequence and then leading back to the source and a restriction in the portion of said fuel line leading back to the source.
 3. In a carburetor, primary and secondary systems respectively having primary and secondary air intake passages, throttle valve means controlling said primary and secondary air intake passages, primary and secondary closed fuel chambers, primary and secondary fuel passages respectively leading from said primary and secondary fuel chambers to said primary and secondary air intake passages, primary and secondary fuel inlet passages to said respective primary and secondary chambers, fuel valves controlling the flow of fuel respectively from said primary and secondary fuel inlet passages to said primary and secondary fuel chambers, and pressure balance tube passage means connecting said primary and secondary chambers balancing pressures therein and placing the same in communication with one another.
 4. The structure defined in claim 3, wherein said balance tube passage means has a restriction therein.
 5. In a carburetor, an air intake passage, a throttle valve controlling said air intake passage, a fuel passage leading into said air intake passage, an air valve in said air intake passage upstream from said throttle valve, and yieldable means urging said air valve to closed position, said air valve being adapted to open against the action of said yieldable means in response to vacuum in said air intake passage, said yieldable means including a rod connected to said throttle valve, a pin having A lost-motion connection with said air valve, and spring means between said rod and pin.
 6. In a carburetor, a primary air intake passage, a primary throttle valve controlling said air intake passage, a primary fuel passage leading into said air intake passage, a primary air valve in said air intake passage upstream from said throttle valve adapted to open in response to vacuum in said air intake passage, means providing a connection between said throttle valve and said air valve to open said air valve in response to opening movement of said throttle valve, said connection means including spring means imposing a yielding closing bias on said air valve with a force dependent upon the position of said throttle valve.
 7. The structure defined in claim 6, wherein said connection means includes a first member connected to one of said valves, a second member connected to the other of said valves, and spring means between said first and second members.
 8. In a carburetor, a primary air intake passage, a primary throttle valve controlling said air intake passage, a primary fuel passage leading into said air intake passage, a primary air valve in said air intake passage upstream from said throttle valve adapted to open in response to vacuum in said air intake passage, means providing a connection between said throttle valve and said air valve to open said air valve in response to opening movement of said throttle valve, said connection means including spring means imposing a yielding closing bias on said air valve when said throttle valve is in curb-idle position, said air valve being substantially fully open when said throttle valve is at a part-throttle position.
 9. The structure defined in claim 8, including a secondary air intake passage, a normally closed secondary throttle valve in said secondary air intake passage, a secondary air valve in said secondary air intake passage upstream from said secondary throttle valve adapted to open in response to vacuum in said secondary air intake passage, a secondary fuel passage leading to said secondary air intake passage between said secondary throttle valve and said secondary air valve, and a lost-motion connection between said primary throttle valve and said secondary throttle valve to open said secondary throttle valve in response to opening movement of said primary throttle valve past said part-throttle position in which said primary air valve is substantially fully open.
 10. The structure defined in claim 9, including a secondary fuel valve controlling the flow of fuel to said secondary fuel passage, means subject to the vacuum in said secondary air intake passage for moving said fuel valve in an opening direction in response to an increase in vacuum and in a closing direction in response to a decrease in vacuum, and means for maintaining said secondary fuel valve open a predetermined minimum amount dependent upon the position of said secondary air valve regardless of the vacuum in said secondary intake passage.
 11. In a carburetor, a primary air intake passage, a primary throttle valve controlling said primary air intake passage, a fuel passage leading to said primary air intake passage, a secondary air intake passage, a normally closed secondary throttle valve in said secondary air intake passage, a secondary air valve in said secondary air intake passage upstream from said secondary throttle valve, a secondary fuel passage leading to said secondary air intake passage between said secondary throttle valve and said secondary air valve, a fuel valve controlling the flow of fuel to said secondary fuel passage, means subject to the vacuum in said secondary air intake passage for moving said fuel valve in an opening direction in response to an increase in vacuum and in a closing direction in response to a decrease in vacuum, and means for maintaining said secondary fuel valve open at least a predetermined amount dependent upon the position of said secondary air valve regardless of and independently of the vacuum in said secondary air intake passage.
 12. In a carburetor, a primary air intake passage, a primary throttle valve controlling said primary air intake passage, a fuel passage leading to said primary air intake passage, a secondary air intake passage, a normally closed secondary throttle valve in said secondary air intake passage, a secondary air valve in said secondary air intake passage upstream from said secondary throttle valve, a secondary fuel passage leading to said secondary air intake passage between said secondary throttle valve and said secondary air valve, a fuel valve controlling the flow of fuel to said secondary fuel passage, means subject to the vacuum in said secondary air intake passage for moving said fuel valve in an opening direction in response to an increase in vacuum and in a closing direction in response to a decrease in vacuum, and means for maintaining said secondary fuel valve open a predetermined amount dependent upon the position of said secondary air valve regardless of the vacuum in said secondary air intake passage, said last-mentioned means including a member movable in one direction to open said fuel valve, and a yieldable connection between said secondary air valve and said member.
 13. In a carburetor, a primary air intake passage, a throttle valve controlling said air intake passage, a fuel passage leading into said air intake passage, an air valve in said air intake passage upstream from said throttle valve adapted to open in response to vacuum in said air intake passage, yieldable means resisting opening movement of said air valve with a force dependent upon the position of said throttle valve, and means for increasing the force of said yieldable means in response to a decrease in temperature and for decreasing the force of said yieldable means in response to an increase in temperature.
 14. In a carburetor, a primary air intake passage, a throttle valve controlling said air intake passage, a fuel passage leading into said air intake passage, an air valve in said air intake passage upstream from said throttle valve adapted to open in response to vacuum in said air intake passage, yieldable means resisting opening movement of said air valve with a force dependent upon the position of said throttle valve, said yieldable means including a rod, a pin having a lost-motion connection with said air valve, spring means between said rod and pin adapted to apply a closing bias on said air valve through said pin, a connection between said rod and throttle valve including a temperature sensitive element, said element upon a drop in temperature moving said rod to increase the tension of said spring means and hence the closing bias on said air valve and upon a rise in temperature moving said rod to decrease the tension of said spring means and hence the closing bias on said air valve.
 15. The structure defined in claim 14, wherein said temperature sensitive element is a bimetal strip.
 16. In a carburetor, a primary air intake passage, a throttle valve controlling said air intake passage, a fuel passage leading into said air intake passage, an air valve in said air intake passage upstream from said throttle valve adapted to open in response to vacuum in said air intake passage, yieldable means resisting opening movement of said air valve with a force dependent upon the position of said throttle valve, said yieldable means including a rod, a pin having a lost-motion connection with said air valve, spring means between said rod and pin adapted to apply a closing bias on said air valve through said pin, means providing a connection between said rod and throttle valve, and a temperature sensitive device incorporated in said rod operable to alter the effective length of said rod in response to temperature changes such that the tension of said spring means and hence the closing bias thereof is increased upon a drop in temperature and is decreased upon a rise in temperature.
 17. The structure defined in claim 16, wherein said temperatuRe sensitive device is a capsule containing a thermally expansible material. 